Process of preparing pig iron in highly-heated mixers



Patented Apr. 17, 1928.

UNITED STATES KARL STOBRAWA, OF GLEIWITZ, GERMANY.

Pnocnss or PREPARING PIG men IN HTGHLY-HEATED mrxnns'.

No Drawing. Application filed January 22, 1927, Serial No. 162,932, and in Germany February 16, 1926.

It is well known that the preliminary treatment of liquid pig-iron may be accomplished in the so-called fiat hearth mixer by means of the ore preliminary refining proc- 5 css, for the purpose of reducing the percentage of the metalloids Si, Mn, C and P in the pig-iron, thus accelerating the preparation in the final oven, and shortening and equalizing the finishing process in the open hearth or Martin oven as much as possible.

It is also well known that in this process shortly after the operation of the flat hearth mixer has commenced, the major portion of manganese besides siliciuni will be removed from the pig-iron, and mixes with the slag or clinker and therefore will be lost for the process in the finishing oven, whereby the metallurgical course of the finishing process and the quality of the final product'may be unfavorably aflected. In order to obtain a mixer product having all the required qualities, the pig-iron used for performing said ore refining process should, for the above mentioned reasons, be of a well determined composition, particularly it should be poor in sulphur, that is a special pig-iron which cannot be used for other purposes.

-A notable progress in the previous treatment of pig-iron within the fiat hearth mixer would consist in that any kind of pigiron in the trade could be used. In practice it has also beenfound that the continuous Work of preparation accomplished by the flat hearth mixer must -be limited in a certain way inorder to not affect the security of operation of this mixing oven, as the hearth as well as the walls of the oven will be heavily attacked by a prolonged preparation.

Such a mixing product contains among others an average-percentage of:

C=about 23-35% Mn=about 0.3-0.4?

Si=about 0.1%. 7

Such a product of flat hearth mixer prod net is already more convenient for subsequent treatment in the Martin or open hearth oven (liquid process) than pig-iron directlly proceeding from blast-furnaces because it contains less slag forming substances. However the refining of such an interme diate product still always requires a considerable' addition of oxidizing and calcareous materials, whereby larger quantitiesof slags or clinkers will be formed which must be carried through the whole process and will considerably retard the time of the whole process, as the thick layer of slags will I prevent an intensive transmission of heat between the metal contents of the oven and the flames of the Martin or open hearth oven. In the proportions in which the percentage of the main slag forming materials, the metalloids C, Mn, P and Si are reduced, I may reduce the oxidizing and calcareous additlons and thus-obtain a thinner layer of slags more rich in oxide, which secures the necessary conditions for a rapid and intensive prt gress of the refining process in the finishing oven. It is well known that in the Martin or open hearth oven the full advantages resulting by the applying of the liquid process that is an increased production and reduced expense of coal may be obtained only if a suitable liquid material may be supplied to said Martin or open hearth oven.

In order to prepare such a liquid material, it is suggested according to my present invention to use the flat hearth mixer (highly heated mixer), for the preliminary preparation or treatment of pig-iron; it is well known that said mixer, in contradistinction to any other mixing devices enables heating gases as well as combustion air to be recovered; in order to save the brick work of the oven, avoid the disagreeable corrosion of the hearth thereof, obtain the major portion of manganese of pig-iron, obtain a mixing product with a minlmum percentage of slag forming materials and determinate compositions, and increase the production of the flat hearth mixer, all this bein' attained, according to the invention, by adding to the pig-iron, highly heated pig-iron waste in convenient amounts such pig-iron waste as herein referred to being understood to be low carbon scrap iron.

The addition of cold pig-iron waste to a mixer bath is alread knownhowever in this working metho comparativel small quantities of Waste iron only can e supplied to the contents of the oven and therefore a slight reduction only of the percentage of metalloids may be obtainedg On the other hand owing to the slow smelting of the cold waste iron the major rtion of the ion manganese will be lost by oxidation; it will previously heated waste iron added to the' crease the. production material will be effected extremely rapidly and accomplished in the Well known way, that is upon the bringing together of these additions poor in carbon and which separately are not easily fusible, with the metallic contents of the oven of about 22.5% of C., the carburatlon of the previously heated waste iron poor in carbon will be effected immediately whereby the melting temperature thereof will be considerably lowered; therefore'the formation of a pig-iron like body will take place, which immediately after its formation will be dissolved in the bath rich in carbon.

The use of additions poor in carbon in a fluid state (pig-iron waste or the like) for the reduction of the percentage of metalloids in the pig-iron is well known; however the carrying into practical effect of such use requires large devices (converters or Martin ovens) and maximum temperatures, whilstaccording to my present process the same purpose-reduction of the percentage of metalloids in pig-iron without melting the latter as such-will be attained without it being necessary to melt the waste iron as such, by accumulating most inexpansive heat in the solid additions by means of simple devices and low temperatures and supplying the fiat hearth mixer with such heat.

It has also been proposed to make use. of iron sponge in the preliminary pig-iron treatment within the mixer; however, for performing the process according to the presentinvention, such iron sponge cannot be used, because it heating at 800 to 1000 C. p

As a substitute for the unsafe ore refining process I use according to this invention, in

the flat hearth mixer a simple pig-iron waste I melting process which does not attack the hearth and walls of the oven, which will inof the mixer. does not drive the manganese contents out from pigiron into the slag and enables the sulphur to be eliminated from the bath" For carrying the new process of preliminarily treating pig-iron in the highly heated mixer into practical effect, the pre-heating of the metallic additions (pigiron waste) is produced by means of a source of heat independent from the Martin or open hearth oven and which operated with most inexpensive heating fluids, such as coal dust, blast-furnace and coke-oven gases and the like, will heat such additions to the highest possible temperature, which however will be below the melting temperature thereof. The more such temperature will be close to the melting temperature, the greater will be the production of the flat hearth mixer and the larger may be quantity of metallic additions, the greater will be'the reduction burns at the preliminary a little oxidizing addition.

of carbon in pig-iron. In order to make pig-iron continuous, I manufacture for instance in flat hearth mixer of 150 tons first a mixer contents of about 130 tons of pigiron-and previously heated waste ingot-ir0n of about the following composition:

C=about 2%.

Mn=about 1.5-2%.

To these mixer contents I add: about 12 tons of liquid pig-iron, about 8 tons of previously heated metallic additions (waste ingot-iron). By the action of the flames in the oven and the heat stored in the mixer contents these previously heated additions Will be converted after a short time into a pig-iron like easily liquid body and the new pig-iron added will be brought to a higher temperature; The total contents of 150 tons will then have substantially the same composition as the initial bath:

C=about 2%.

Mn=about 1.52%.

Now about 20 tons of this intermediate product may be taken from the mixer and brought into the finishing oven for subsequent treatment. 7

Further additions of about 12 tons liquid pig-iron and about 8 tons previously heated waste iron and the removal of a corresponding quantity of about 20 tons from the mixer contents will result into the continuous new flat hearth mixer process. The silicium contents of the pig-iron, as is well known, will be removed from the mixer bath by the action of the basic slag and if necessary by In the new process of preliminary treating pig-iron the. unsafety of operation of the flat hearth mixer will be avoided, the mixer contents may be increased according'to requirements and therefore the weight 'of the mixer charge also.

Having now fully described my said invention, what I claim and desire to secure by Letters Patent, is:

A process for preheating pig-iron in the flat hearth mixer (highly heated mixer) consisting' in supplying to the pig-iron, which latter is rich in carbon, low carbon scrap lit iron preheated at a temperature as close as possible to the melting point by means of a source of heat independent from the mixer.

whereby an immediate carburation of said low carbon scrap iron and a lower melting point of same occurs in order to maintain substantially constant the percentage pf manganese contained in the pig-iron to be treated and to diminish accordingly the percentage of silicon. carbonand phosphorus.

In testimony whereof I have hereunto set my hand.

KARL STOBRAVVA; 

